The desirability for "bandwidth tracking" as disclosed herein arises from a system requiring maximum signal-to-noise ratio in conjunction with a rather large range in operating frequency, such as a magnetic recording/play back system. A fixed bandwidth (upper cutoff frequency) based on maximum operating frequency would result in comparatively poor signal-to-noise ratio at the minimum operating frequency. Alternatively, a fixed bandwidth based on minimum operating frequency would be inadequate for higher frequency operation.
U.S. Pat. No. 4,446,493 discloses a variable frequency response equalizer which varies the time constant associated with the equalizer based on amplified signal. The magnitude of the time constant is reduced when the level of the signal amplified becomes lower than a predetermined value. Such a solution, as well as the approaches described in other patents of interest, i.e. U.S. Pat. No. 4,479,152, and U.S. Pat. No. 4,633,200 present the drawback of requiring very complex and sophisticated circuitry comprising transistors, delay means, switchable networks, voltage controlled amplifiers, etc.